Original Article Causes of Excessive Blinking in Children Aged 4-12 Years

Int J Clin Exp Med 2019;12(8):10747-10754 www.ijcem.com /ISSN:1940-5901/IJCEM0094898

Original Article Causes of excessive blinking in children aged 4-12 years

Ru-Lian Zhao, Yang Wang, Min Liu, Yong Li, Lian-Hong Pi

Department of Ophthalmology, Children’s Hospital, Chongqing Medical University, Chongqing 400014, China Received April 4, 2019; Accepted June 10, 2019; Epub August 15, 2019; Published August 30, 2019

Abstract: The current study aimed to investigate causes of excessive blinking in children aged 4 to 12 years, provid- ing evidence for clinical treatment of abnormal blinking in children. A total of 578 children complaining of excessive blinking were recruited. Moreover, a total of 370 children without excessive blinking served as controls. Results showed that children with excessive blinking might have a single etiology or multiple etiologies together. Occurrence of excessive blinking was negatively correlated with age (P<0.001) and affected by sex (P=0.008). There were significant differences in tear break-up times (P<0.001), allergic conjunctivitis (P<0.001), corneal epithelial injuries (P=0.013), diopters of children with ametropia (P=0.001), and times of video display terminal (P<0.001) between three age groups. Allergic conjunctivitis (P<0.001), positive corneal fluorescein staining (P<0.001), conjunctival lithiasis/trichiasis (P<0.001), and times of video display terminal (P<0.001) had a negative relationship with breakup times of tear film. Allergic conjunctivitis and conjunctival lithiasis/trichiasis showed positive relationships with corneal fluorescein staining (P<0.001). Times of video display terminal were positively related to diopters of myopia- related ametropia (P=0.001). All subjects had mild ametropia. In addition, there were significant differences in breakup times of tear film between children with excessive blinking and controls (P=0.047). Thus, ocular surface diseases, refractive problems, times of video exposure, and tic disorders are causes of excessive blinking. Of these factors, ocular surface diseases and times of video exposure have relationships with breakup times of tear film. Moreover, these factors may interact with each other, causing deterioration of excessive blinking.

Keywords: Child, blinking, breakup times of tear film, ocular surface disease, times of video display terminal, tic disorders

Introduction eyebrows, wrinkling the forehead, and sucking the nose. Excessive blinking has become a Blinking occurrence is normally about 10-15 common disease in the Department of Pediatric blinks/minute. Each blink lasts for 0.3-0.4 sec- Ophthalmology. In some children, excessive onds, with an interval of 3-4 seconds between blinking is misdiagnosed as infectious kerato- blinks. Blinking is a natural neural reflex of the conjunctivitis, causing long term use of eye eyelid. It plays an important role in adaptive drops after misdiagnosis. This may increase human behaviors [1]. Excessive blinking is de- incidence of ocular discomforts and injuries. It fined as a frequency of blinking higher than 15 may even cause side effects of some drugs [5, blinks/minute [2, 3]. Excessive blinking is of- 6]. Some parents do not pay attention. This may ten accompanied by ocular symptoms (such as contribute to deterioration of the disease and itchy eyes, foreign body sensation of the eyes, delay correct treatment. In addition, some par- ocular fatigue, and photophobia) and charac- ents become nervous about this disease and terized by excessive unilateral or bilateral eyelid misdiagnose it as “tic disorder”. Thus, some closure and opening with or without abnormal inhibitory drugs have been used for treatment eyeball movement. Excessive blinking is often of excessive blinking. These may not only ca- intermittent and recurrent. It is difficult to con- use side effects, but also bring adverse somat- trol. In addition, it may be attenuated during ic and psychological effects [7]. It usually gazing and disappear after blinking for several causes significant psychological burden to chil- weeks or months. It may recur after disappear- dren and their parents. Doane and others [8, 9] ance [4]. Some children with excessive blinking aimed to identify the mechanical properties of develop other symptoms, such as crowing the blinking. Blinking phenomena have been exten- Excessive blinking in children sively studied in various contexts of disease, Exclusion criteria: (1) Children did not cooper- such as dry eyes and visual tasks, as well as ate with examinations; (2) Parents or guardians systemic disease [10, 11]. Causes of excessive refused to participate in this study; (3) Children blinking are complex. They may include ocular were allergic to fluorescein; and (4) Children disease, systemic disease, and psychological received treatment for excessive blinking be- disease [12]. Excessive blinking has significan- fore the study. tly affected the learning abilities of children. Despite a plethora of information concerning Methods and data processing blinking disorders in adulthood, relatively little information exists for evaluation and manage- The following information was collected by in- ment of children presenting with blinking disor- terviewing parents or guardians: (1) Gender, ders. Nonstandard diagnosis and treatments age, duration, and frequency of signs and symp- of excessive blinking also cause significant ad- toms; (2) History of allergies, including the fam- verse effects in children and their families. The- ily history of allergies and allergic diseases; (3) refore, more attention should be paid to the Concomitant focal and systemic symptoms dur- diagnosis and treatment of children with exces- ing excessive blinking; (4) Diagnosis of tic dis- sive blinking. Thus, it is imperative to investi- orders; (5) Prior diagnosis and treatment of gate and identify causes of excessive blinking, excessive blinking and use of eye drops or anti- taking targeted treatment. This may assist in biotics; and (6) Times of video display terminal avoiding misdiagnosis and mistreatment. (VDT) each day.

The current study investigated children with Slit-lamp examination: (1) Routine eye examina- excessive blinking. Possible causes of exces- tion: Eyelids, eyelashes, conjunctiva, and cor- sive blinking were explored in these children, nea were examined for papilla, follicles, stones, aiming to provide evidence for clinical treat- injury, inflammation, foreign bodies, and scars; ment of abnormal blinking in children. (2) Tear meniscus height (TMH): Abnormal tear secretion was defined as TMH lower than 0.3 Materials and methods mm; (3) Breakup times of tear film (BUT): BUT General characteristics was measured thrice and the mean was calculated. Decreases in tear film stability were This study adhered to the tenets of the De- defined as BUT lower than 10 seconds; and (4) claration of Helsinki and was approved by the Corneal fluorescein staining (FLS): Positive st- Institutional Review Board of Children’s Hos- aining suggests corneal epithelial injury [13]. pital, Chongqing Medical University. Consent for publication was obtained from all partici- Allergen examination: Skin prick tests were pants. employed to examine common inhaled allergens. A positive reaction is defined as a light This study was conducted on children present- yellow rash with surrounding erythema. History ing to the Ophthalmology Clinic with excessive of allergies, family history of allergies, eye ex- blinking. The study was conducted between aminations, and allergen examinations were December 2016 and November 2018. A total employed for diagnosis of allergic conjuncti- of 578 children, including 341 boys and 237 vitis (AC) [14]. girls, with excessive blinking ages from 4 to 12 years old, served as the observation group. In Vision examination: The International Visual addition, 370 matched children without exces- Chart was used for vision examinations. When sive blinking, including 220 boys and 150 girls, visual acuity was ≤0.6 for children aged 4 years were randomly recruited as controls. and ≤0.8 for children aged ≥5 years, abnormal visual acuity was diagnosed [15]. Inclusion criteria: (1) Children with excessive blinking as the chief complaint; (2) Informed Autorefractor (RK-8100; Topcon, Tokyo, Japan): consent was obtained from parents or guard- This was performed three times and the mean ians; (3) Children cooperated with examina- was calculated. When vision examinations and tions; and (4) Children did not receive prior autorefractors indicated abnormal, cycloplegic treatment for excessive blinking. retinoscopy procedures were performed.

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Table 1. Numbers of TD and AC of 3 groups in the observation group tropia, and tic disor- TD AC ders with BUT were Group Boy Girl Boy Girl Boy Girl also explored. Relati- onships between aller- 4-6 y 171 100 8 3 116 (67.84%) 48 (48.00%) gic conjunctivitis, con- 7-9 y 114 92 5 2 52 (45.61%) 34 (36.96%) junctival lithiasis/trich- 10-12 y 56 45 3 2 20 (35.71%) 13 (28.89%) iasis with positive FLS, Total Number 341 237 16 7 188 (55.13%) 95 (40.08%) and times of video dis- Proportion 59.00% 41.00% 2.77% 1.22% 32.52% 16.43% play terminal with ty- Total proportion 100.00% 3.99% 48.95% pes of ametropia were Notes: observation group: children with excessive blinking; AC: allergic conjunctivitis; TD: Tic also explored. P<0.05 disorder. indicates statistical significance.

Cycloplegic retinoscopy: 1% Atropine sulfate Pearson’s correlation analysis included the eye gel was used three times a day for 3 days amount of frequent blinking and ages of the to the children <7 years; 1% cyclopentolate children. BUT and times of video display termi- was used three times with the interval of 10 nal were also included, as well as times of video minutes for children ≥7 years. Pupillary reac- display terminal and diopters of ametropia. tions were then tested. Cycloplegia is defined P<0.05 indicates statistical significance. as absence of pupillary light reflex. Streak reti- noscope (YZ24; Six Six Vision Corp, Suzhou, Paired-t tests were employed for comparisons China) was used for retinoscopy [16]. of BUT between children with and without excessive blinking, as well as gender. P<0.05 indi- Hyperopia is defined as spherical degree ≥ cates statistical significance. +2.00 D. Myopia is defined as spherical degree ≤-0.50 D. Astigmatism is defined as absolute Results cylindrical degree ≥1.00 DC. The diopter is rep- resented by Spherical equivalent refraction A total of 578 children with excessive blinking (SER). Diopters ≤-3.00 D is mild refractive error, were enrolled as the observation group. This -3.00 D~-6.00 D is moderate refractive error, group included 341 boys (59.00%) and 237 girls (41.00%). The mean age was (6.99±2.26) and ≥-6.00 D is high refractive error. The_ distri- bution of refraction is expressed as x ± s years old (4-12 years). In addition, there were [17-19]. 370 children without excessive blinking serv- ing as the control group. This group included Statistical analysis 220 boys (59.45%) and 150 girls (40.55%). The mean age was (7.02±2.30) years old (4-12 Children with excessive blinking in the observa- years). tion group were divided into three age groups, including the 4-6 group, 7-9 group, and 10-12 Of children with excessive blinking, allergic con- group. Children without excessive blinking ser- junctivitis was found in 283 children (48.95%; ved as controls. All data were categorically re- 188 boys and 95 girls) (Table 1). Allergen ex- corded, listed, and subjected to statistical an- aminations showed that most children were alysis with SPSS version 22.0. Count data are allergic to dust mites (61.23%) (dermatophagoides pteronyssinus and dermatophagoides fa- expressed as _rates (%). Measurement data are described by x ± s. rinae). Conjunctival lithiasis/trichiasis was not- ed in 37 children (6.40%; 22 boys and 15 girls). Spearman’s rank correlation analysis was ad- Tic disorders (TD) were found in 23 children opted to investigate the relationships of BUT, (3.99%; 16 boys and 7 girls) (Table 1). Positive allergic conjunctivitis, conjunctival lithiasis or FLS was shown in 247 children (42.73%; 143 trichiasis, positive FLS, times of video display boys and 104 girls) (Table 2). terminal, diopters of ametropia, and tic disorders between the 3 age groups. Relationships Ametropia was observed in 78 children between gender, allergic conjunctivitis, con- (13.49%; 45 boys and 33 girls). All cases were junctival lithiasis or trichiasis, positive FLS, ti- mild ametropia. Diopters of ametropia in the mes of video display terminal, diopters of ame- three groups were, respectively, (1.47±1.61) D,

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Table 2. FLS and conjunctival lithiasis/trichiasis of 3 groups in the observation group FLS Lithiasis/trichiasis Group Boy Girl Boy Girl 4-6 y 79 (46.20%) 52 (52.00%) 11 (6.43%) 7 (7.00%) 7-9 y 45 (39.47%) 38 (41.30%) 8 (7.01%) 5 (5.43%) 10-12 y 19 (33.92%) 14 (31.11%) 3 (5.36%) 3 (6.66%) Total Number 143 (41.93%) 104 (43.88%) 22 (6.45%) 15 (6.32%) Proportion 24.74% 17.99% 3.81% 2.59% Total proportion 42.73% 6.40% Notes: observation group: children with excessive blinking; FLS: fluorescein staining.

Table 3. Ametropia and VDT times of 3 groups in the observation group Group Boy Girl Hypermetropic Myopic Diopter (D) VDT (h/d) 4-6 y 20 (11.69%) 12 (12.00%) 26 (9.59%) 6 (2.21%) 1.47±1.61 1.27±0.55 7-9 y 9 (7.89%) 8 (8.69%) 7 (3.40%) 10 (4.85%) -0.49±1.37 2.08±0.87 10-12 y 16 (28.57%) 13 (28.88%) 4 (3.96%) 25 (24.75%) -1.00±1.10 2.82±0.94 Total 45 (13.19%) 33 (13.92%) 37 (6.40%) 41 (7.09%) Proportion 13.19% 13.92% 6.40% 7.09% Notes: observation group: children with excessive blinking; VDT: video display terminal.

Table 4. BUT and TMH of 2 groups in the observation group Total (n) BUT (s) TMH Age Observation Control Observation Control Observation Control (n=578) (n=370) (n=578) (n=370) (n=578) (n=370) 4-6 y 271 173 8.57±2.77 9.34±2.14 0.32±0.040 0.33±0.023 7-9 y 206 129 8.44±2.49 8.89±1.65 0.33±0.043 0.32±0.033 10-12 y 101 68 7.87±1.86 8.25±1.93 0.32±0.041 0.32±0.039 Notes: observation group: children with excessive blinking; BUT: breakup time of tear film;observation: children with frequent blinking as the observation group; control: children without frequent blinking as the control; TMH: tear meniscus height.

(-0.49±1.37) D, and (-1.00±1.10) D (Table 3). age and affected by sex (Figure 1). Table 6 out- Times of video display terminal in the three lines correlation analysis statistics of different groups were, respectively, (1.27±0.55) h/d, groups and correlative factors. (2.08±0.87) h/d, and (2.82±0.94) h/d (Table 3). Discussion

In children with excessive blinking, BUT was, Reports of excessive blinking in children are respectively, (8.57±2.77) s, (8.44±2.49) s, and infrequent. Very little guidance exists concern- (7.87±1.86) s. BUT in children without frequ- ing how to evaluate and manage children with ent blinking was, respectively, (9.34±2.14) s, excessive blinking. However, excessive blinking (8.89±1.65) s, and (8.25±1.93) s (Table 4). has become a common disease in the De- TMH of all was higher than 0.3 mm (Table 4). partment of Pediatric Ophthalmology. In this study, it was found that occurrence of exces- The course of the disease in children with fre- sive blinking was negatively correlated with quent blinking was (1-90) days. age. Excessive blinking decreases with increas- es in age. This is mainly due to the blink reflex Children with frequent blinking may have a sin- and childhood anatomy, as well as physiologi- gle cause or multiple causes (Table 5). In chil- cal characteristics. The sensor of the blinking dren with excessive blinking, occurrence of fre- reflex is the cornea. It is controlled by the cen- quent blinking was negatively correlated with tral nervous system [20]. In children, the cere-

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Table 5. Causes of excessive blinking reduces, the friction may Causes of excessive blinking Number Proportion increase during eyeball mo- Simple shortened BUT 121 20.93% vement. This may cause damage to the corneal epithe- Shortened BUT and positive FLS 61 10.55% lium. BUT in children with AC and shortened BUT 104 17.99% excessive blinking was lo- AC, shortened BUT and positive FLS 154 26.64% wer than controls. However, AC, and ametropia 6 1.04% TMH showed no significant AC, ametropia and shortened BUT 3 0.52% differences between two AC, ametropia, shortened BUT and positive FLS 4 0.69% groups. This indicates that AC and TD 2 0.35% tear secretion is normal AC, TD and shortened BUT 3 0.52% and tear film instability is a AC, lithiasis/trichiasis and shortened BUT 4 0.69% major cause of excessive blinking. When tear stability AC, lithiasis/trichiasis, shortened BUT and positive FLS 3 0.52% reduces, the cornea beco- Lithiasis/trichiasis and shortened BUT 5 0.87% mes dry soon after the eye- Lithiasis/trichiasis, shortened BUT and positive FLS 25 4.33% lid opens. Excessive blink- Ametropia 65 11.25% ing is helpful for the recon- TD 18 3.11% struction of tear film. Tear Total number 578 100% instability may cause exce- Note: BUT: breakup time of tear film; FLS: fluorescein staining; AC: allergic conjunctivi- ssive blinking. Kashkouli et tis; TD: Tic disorder. al. [22] and Nosch et al. [23] found that tear film stability directly affected the frequency of blinking, in ac- cord with present findings. Thus, BUT can be used to reflect the frequency of blinking. Correlation levels of BUT with other factors should be further studied. Results showed that BUT had no relationship with gender, consistent with findings reported by Pauline et al. [24]. BUT is negatively correlated with age, consistent with findings reported by Cho et al. [25]. Figure 1. Number of frequent blinking increased with age and sex. Of children with excessive blinking, the occurrence of frequent blinking was negatively correlated with age (r=-0.944, p=0.000) and affected by sex (T=3.54, p=0.008). Allergic conjunctivitis has become a common disease and a major cause of exces- bral cortex is immature. Thus, over-reaction to sive blinking in children. Incidence of infectious a stimulation is very common. The cornea is diseases has decreased, but incidence of al- rich in sensory nerve endings and sensitive to lergic diseases has increased with improve- stimulation. Corneal sensitivity is high in child- ments in living environments, development of hood, but decreases with age. health care, and increased air pollution [26]. Present results show that allergic conjunctivi- Ocular surface disease: Tear film locates on the tis was negatively related to BUT and positively surface of the cornea and provides a moist to positive FLS. When mast cells and eosino- environment for the epithelium of cornea and phils become activated, they release many in- conjunctiva. This may reduce friction during flammatory factors. This causes damage to cor- blinking and eyeball movement [21]. Positive neal and conjunctival epithelial cells and goblet FLS is negative with BUT (p<0.05). When BUT cells. This may result in a lack of mucus layer,

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Table 6. Correlation analysis statistics Different groups Correlative factor Statistical value P 3 groups of observation BUT r=-0.175 P<0.001 AC r=-0.192 P<0.001 FLS r=-0.103 P=0.013 Diopter of ametropia r=-0.607 P=0.001 Time of VDT r=0.626 P<0.001 Conjunctival lithiasis/trichiasis P>0.05 TD P>0.05 Correlative factors of observation AC and BUT r=-0.814 P<0.001 FLS and BUT r=-0.748 P<0.001 Conjunctival lithiasis/trichiasis and BUT r=-0.311 P<0.001 Time of VDT and BUT r=-0.307 P<0.001 AC and FLS r=0.769 P<0.001 Conjunctival lithiasis/trichiasis and FLS r=0.153 P<0.001 Time of VDT and diopter of myopia r=-0.141 P=0.001 Sex and BUT P>0.05 TD and BUT P>0.05 Observation and control group BUT t=-4.43 P=0.047 TMH P>0.05 Age P>0.05 Gender P>0.05 Notes: Observation: children with excessive blinking; control group: children without excessive blinking; BUT: breakup time of tear film; FLS: fluorescein staining; AC: allergic conjunctivitis;TD: Tic disorder; TMH: tear meniscus height. There were significant differences in BUT, allergic conjunctivitis, corneal epithelial injury, diopter of children with ametropia and time of VDT among the three groups, but no difference in conjunctival lithiasis/trichiasis and tic disorder. Allergic conjunctivitis, positive FLS, conjunctival lithiasis/trichiasis, and time of VDT had a negative relationship with BUT, but TD and sex had no relationship with BUT. AC and conjunctival lithiasis/trichiasis had positive relationships with FLS. Time of VDT was positively related to the diopter of myopia-related ametropia, and all were mild ametropia. In addition, there was a significant difference of BUT between children with excessive blinking and without; The indexes of TMH, age, and gender showed no significant differences between two groups. P<0.05 indicates statistical significance. damage the corneal epithelium, and reduce Ametropia: Simple ametropia was found in 65 tear film stability [27]. Results showed that all- children with excessive blinking. All cases were ergic conjunctivitis had a negative relationship mild ametropia. Excessive blinking was shown with age. Incidence of allergic conjunctivitis to be related to refractive error. In mild ame- was higher in boys (32.52%) than girls (16.43%). tropia, the visual organs are over-regulated for This is consistent with Rhee’s research [28]. compensation, which leads to visual fatigue Results may be related to the fact that boys and frequent blinking. Coats et al. [2] speculat- have a matrilineal tendency and a wider range ed that ametropia without correction was a of activities. Thus, they are easily exposed to major cause of excessive blinking in children. allergens [29]. After correction, excessive blinking was attenuated or even disappeared in about 87% of chil- Conjunctival lithiasis/trichiasis is also a cause dren. Abdi et al. found that correction of ame- of excessive blinking in children. Results sug- tropia improved ocular symptoms in 94% of gest that conjunctival lithiasis/trichiasis was children, attenuated visual fatigue, and im- negatively related to BUT and positively to po- proved excessive blinking [30]. Thus, refractive sitive FLS. Mechanical stimulation induced by problems are also important causes of exces- conjunctival lithiasis/trichiasis may cause da- sive blinking in children. mage to the ocular surface, reduce tear secretion, and damage tear stability, resulting in Tic disorders: Tic disorders are causes of exces- excessive blinking. sive blinking in children. Tic disorder refers to a

10752 Int J Clin Exp Med 2019;12(8):10747-10754 Excessive blinking in children mental disease characterized by motor tics and psychological diseases. There could be a and/or phonic tics [31]. Incidence of TD in boys single cause for excessive blinking in some chil- (2.77%) was higher than that in girls (1.22%). dren, but multiple factors are possible. Active Kurlan et al. found that TD mainly occurred at identification of causes of excessive blinking 2-21 years. Incidence in males was higher than and appropriate treatment methods are impor- that in females [32], consistent with the current tant. Clinicians should aim to avoid misdiagno- study. Some neuroleptics (mainly antipsychotic sis, missed diagnosis, and over-treatment. drugs) are effective in improving tic disorders. However, antipsychotic drugs have some side Disclosure of conflict of interest effects, including cognitive retardation, drug- induced irritability, anxiety, and depression, None. leading to adverse effects on the health of children [7]. Thus, treatment of tic disorders in chil- Address correspondence to: Lian-Hong Pi, Depart- dren should be cautionary. Over-treatment sh- ment of Ophthalmology, Children’s Hospital, Chong- ould be avoided. qing Medical University, Chongqing 400014, China. E-mail: [email protected] Times of VDT (video display terminal): Results showed that times of VDT were negatively relat- References ed to BUT, but positively related to the diopter of myopia. With the development of market [1] Hoppe D, Helfmann S and Rothkopf CA. Hu- mans quickly learn to blink strategically in re- economy and the information era, VDT influ- sponse to environmental task demands. Proc ences lives of people with its ample function. Natl Acad Sci U S A 2018; 115: 2246-2251. Long time use of VDT may increase exposure of [2] Coats DK, Paysse EA and Kim DS. Excessive palpebral fissure and promote the evaporation blinking in childhood: a prospective evaluation of tear film, which may cause dry eye and of 99 children. Ophthalmology 2001; 108: increase the frequency of blinking [33]. In addi- 1556-1561. tion, the characteristics of VDT may increase [3] Conte A, Defazio G, Ferrazzano G, Hallett M, regulatory and convergence movements of the Macerollo A, Fabbrini G and Berardelli A. Is in- eyes for clear vision. This may cause eye dis- creased blinking a form of blepharospasm? comfort and subsequent excessive blinking. Neurology 2013; 80: 2236-2241. You et al. found that myopia was related to the [4] Schicatano EJ. The effects of attention on time interval between two rests during comput- the trigeminal blink reflex. Percept Mot Skills 2016; 122: 444-451. er-related work [34]. Jordan et al. found that [5] Coroi MC, Bungau S and Tit M. Preservatives times of computer-related work in adolescenc- from the eye drops and the ocular surface. es with myopia were 0.7-1.6 hours longer than Rom J Ophthalmol 2015; 59: 2-5. in those with emmetropia [35], consistent with [6] Liu Z and Huang C. [A correct understanding of present findings. preservatives in eye drops]. Zhonghua Yan Ke Za Zhi 2015; 51: 641-644. Excessive blinking is also affected by sex (p= [7] Osland ST, Steeves TD and Pringsheim T. Ph- 0.008). It was hypothesized that this is related armacological treatment for attention deficit to causes of excessive blinking. It was found hyperactivity disorder (ADHD) in children with that allergic conjunctivitis (48.95%) was the comorbid tic disorders. Cochrane Database cause of excessive blinking. Incidence of this Syst Rev 2018; 6: Cd007990. disease was higher in boys than in girls. [8] Doane MG. Interactions of eyelids and tears in corneal wetting and the dynamics of the nor- In conclusion, correlation analysis showed that mal human eyeblink. Am J Ophthalmol 1980; allergic conjunctivitis, corneal epithelial injury, 89: 507-516. conjunctival lithiasis/trichiasis, and times of [9] Stern JA, Walrath LC and Goldstein R. The en- dogenous eyeblink. Psychophysiology 1984; video display terminal were related to BUT. The 21: 22-33. pathophysiology of these ocular surface dis- [10] Collins MJ, Iskander DR, Saunders A, Hook S, eases may affect ocular surface homeostasis Anthony E and Gillon R. Blinking patterns and and disrupt the stability of tear film, increasing corneal staining. Eye Contact Lens 2006; 32: the risk for excessive blinking. Causes of exce- 287-293. ssive blinking are complex in children. They may [11] Torkildsen G. The effects of lubricant eye drops include ocular diseases, systemic diseases, on visual function as measured by the Inter-

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